Diatom monitors of close-to-pristine, very-low alkalinity habitats: three new Eunotia species from springs in Nature Parks of the south-eastern Alps

On the basis of LM and SEM observations as well as of environmental data, three species of the predominantly-acidophilous diatom genus Eunotia (E. cisalpina, E. fallacoides, E. insubrica) are described as new to science, and characterized from the ecological point of view. The three new species were not distinguished from other similar ones in the past but can be identified at the LM by careful observation of diacritical characters such as valve outline (in particular the shape of the endings), dimensions, and stria density. One of the three new species (E. insubrica) presents a very peculiar ultrastructural feature, i.e. well-developed pseudoseptum-like structures at the apices. The three new species were pointed out by detailed analyses of materials sampled in the south-eastern Alps. It is put forward that diatom investigations adopting high-resolution taxonomy are particularly opportune in habitats such as those colonized by the three new species. The three new species were found to be characteristic of low-alkalinity, naturally slightly-acidic, strictly-oligotrophic, high-mountain springs and lakes. Efficient desiccation-resistance strategies, apparently widespread in the genus Eunotia, might be supposed also for the three new species, that were found to thrive also in lowdischarge springs and in the shallow littoral waters of lakes showing seasonal or exploitation-enhanced water-level fluctuations. The diatom assemblages of these aquatic habitats possess a high species richness, and include many rare and Red List species, and are thus of prominent importance for diatom biodiversity conservation. These relatively-pristine aquatic habitats on siliceous bedrocks are however highly sensitive, and endangered because of diffuse pollution. Climate- and environmental-change driven increased release of organic acids, and contamination by airborne inorganic acids and nutrients are all potential threats to these still highintegrity but fragile systems. The detailed characterization of their diatom assemblages, that are excellent monitors of acid-base and nutrient status is thus of the foremost importance. In particular the distinction between naturally-acidic and acidified systems is a relevant topic that might benefit from detailed knowledge of taxonomy and ecology of both communities and indicative taxa of the diatom assemblages

Environmental History of Lago di Tovel, Trento, Italy, Revealed by Sediment Cores and 3.5kHz Seismic Mapping

Proxy data from a total of 30 sediment cores and information from a seismic survey show that the sedimentological and limnological history of Lago di Tovel (1178m a.s.l.) has been significantly influenced by slope dynamics of its mountainous catchment. The lake represents a dead-ice lake with pro-glacial deposits at the base of its sedimentary record. A prominent lake level rise in 1597/1598 that increased maximum water depth from ∼20 to 39m caused slope instabilities, leading to the deposition of mass-flow sediments with a maximum thickness of 2.5m in the northern part of the lake and less than 50cm in the southern part, resulting in a total volume of more than 113,000m3. Consequently, a rough lake bottom morphology was produced, which led to distinct differences in sedimentation rates of 0.07cmyr−1 on sills and 0.18cmyr−1 within depressions. The age of the top of the mass-flow deposits was used to validate the ages of the younger, laminated sediments, which were dated by 210Pb and 137Cs. Lithological investigations showed that the sediments below the mass-flow deposits are also laminated and that they were not bioturbated. The long-term meromixis of Lago di Tovel is therefore mainly due to a combination of its topographic setting and the 5-month period of ice cover. Both prevent effective mixing of the lake by strong winds during spring and autumn. Distinct spatial differences in sediment distribution within the lake show that it is risky to interpret proxy data from only one coring site, even if the lake is very small. This is especially true in mountainous areas, where rock falls, mass movements, and slope instabilities of a significant size may have considerable effects on lake

A Simple and Inexpensive Method to Gain Diatom Absolute Abundances from Permanent Mounts in Hydrobiological and Paleoecological Research

This article belongs to the Special Issue Advances in Hydrogeology[Abstract] Here, we describe and discuss a method based on microscopical field of view (FOV) area to estimate diatom absolute abundances (densities or concentrations), and we statistically verify its reliability, also comparing it to another commonly used method (microspheres). To test the new method, we purposely performed replicate counts, both with the FOV and with the microsphere method, on both subfossil and recent material (samples) from mires. Intraclass correlation (ICC) revealed a high degree of agreement between the measurements obtained for the replicates with each of the two methods, suggesting that both are reliable for measuring diatom valve concentrations. However, the FOV consistently overestimated diatom absolute abundances, as compared to the microsphere method, and the ICC value used to assess the reliability of the two methods combined suggested that the two methods cannot be used interchangeably. The FOV method is relatively simple, has a lower cost, wider applicability, higher resolution, and warrants compatibility with existing datasets. However, there may also be drawbacks, such as the potential for sample distortion during the concentration process. Therefore, it is important to carefully evaluate the strengths and limitations of the different methods before adopting one for specific research or applied questions

A Simple and Inexpensive Method to Gain Diatom Absolute Abundances from Permanent Mounts in Hydrobiological and Paleoecological Research

Here, we describe and discuss a method based on microscopical field of view (FOV) area to estimate diatom absolute abundances (densities or concentrations), and we statistically verify its reliability, also comparing it to another commonly used method (microspheres). To test the new method, we purposely performed replicate counts, both with the FOV and with the microsphere method, on both subfossil and recent material (samples) from mires. Intraclass correlation (ICC) revealed a high degree of agreement between the measurements obtained for the replicates with each of the two methods, suggesting that both are reliable for measuring diatom valve concentrations. However, the FOV consistently overestimated diatom absolute abundances, as compared to the microsphere method, and the ICC value used to assess the reliability of the two methods combined suggested that the two methods cannot be used interchangeably. The FOV method is relatively simple, has a lower cost, wider applicability, higher resolution, and warrants compatibility with existing datasets. However, there may also be drawbacks, such as the potential for sample distortion during the concentration process. Therefore, it is important to carefully evaluate the strengths and limitations of the different methods before adopting one for specific research or applied questions

Congruencies between photoautotrophic groups in springs of the Italian Alps: implications for conservation strategies

Even though a number of studies have demonstrated the importance of photoautotrophic organisms in spring habitats, investigations that consider several photoautotrophic taxonomic groups are lacking. Within the framework of a multidisciplinary project on springs of the south-eastern Alps, we studied algae, diatoms, lichens, and bryophytes and (1) compared the alpha, beta and gamma diversity, and the composition of the studied groups between carbonate and siliceous springs, (2) estimated the nonrandomness of species combinations within organismal groups, and (3) examined the congruence in species assemblage patterns across taxonomic groups. In 40 springs, 69 species of algae, 110 species of diatoms, 29 species of lichens, and 62 species of bryophytes were found. Diatoms, lichens and bryophytes had higher species-richness in siliceous springs, while other algae had higher richness in carbonate springs. For all taxonomic groups, carbonate and siliceous springs host different assemblages, indicating that both types of substrata contribute to the overall regional diversity of spring photoautotrophs. In individual springs, the photoautotroph groups are characterised by a similar proportion of species of their regional pool, and form relatively speciespoor communities with a high turnover of species among springs. This pattern has important implications for conservation, suggesting that the protection of single sites might not be effective, and that a biodiversity conservation plan for spring habitats should be developed at the regional level, and include a network of sites. Interestingly, the co-occurrence indices suggested that, in individual springs, stochastic processes might the most important mechanisms in the establishment of local assemblages. A weak cross-taxon congruency was found, suggesting that a single taxon surrogate will not adequately represent other photoautotrophic groups. Therefore, spring conservation plans for photoautotrophs should not use one group as a surrogate for overall photoautotrophic diversity, but should adopt the use of different taxonomic groups

Using different epilithic-diatom assemblage metrics for an ecological characterization of the shores of Lake Garda

It has been proved that littoral diatoms provide a useful marker for detecting localised changes resulting from neve anthropogenic disturbances or intermittent releases of sewage along the shorelines of lakes. This study tested the spatial resolution at which this general observation occurs, by selecting areas with different anthropogenic pressures (urbanization) along a latitudinal gradient in Lake Garda, a deep and wide peri-Alpine lake. The sampling design aimed to detect differences in diatom distribution in terms of species diversity, quality indices, proportion of Red List taxa, assemblages, and individual species. Because the extent to which diatom assemblages respond to these gradients was unknown, we used assemblage metrics of different sensitivities. Results showed that the most important environmental factor was the latitudinal gradient, which was revealed by almost all the assemblage metrics. This dominant trend was explained by two co-occurring environmental gradients: concentration of nutrients and thermal gradient. The importance of different levels of urbanization was unevenly partitioned among locations and latitudes because of the different intensities of urbanization pressure. Only the species Brachysira neglectissima, the quality index (Trophic Index), and to a lesser extent, the metric at assemblage level revealed significant effects. Overall, this study comes to two main conclusions: (1) different metrics are needed to detect the multifaceted effects of anthropogenic disturbances, which by their very nature are unevenly distributed and of different intensities, and therefore affect assemblages to different degrees; (2) for any monitoring program in this lake to be effective, the various gradients revealed in this work should be taken into account. Failing to include these sources of variability might lessen the benefits of monitorin

Diatom communities and vegetation of springs in the south-western Alps

Springs are unique but understudied habitats. Diatom communities have received some attention but have remained largely unknown in the south-western Alps. We therefore studied the springs of the south-western extreme of the Alpine mountain range. We analysed epilithic and epiphytic assemblages in 48 springs of different ecomorphological types, located on contrasting lithological substrata (carbonate/siliceous). Moreover, phytosociological relevés were carried out for carbonate springs. The diatom flora consisted of 223 taxa. Most (198) of the taxa were included in the Red List, and 12.5% belonged to threatened categories. Characteristic spring taxa (crenophiles) were present. The ecological preferences of crenophilous diatom species described in the eastern Alps were confirmed. Diatom species characteristic of the lake-littoral zone were found in pool springs. We observed no significant differences in species richness and diversity between epilithic and epiphytic assemblages, but some species showed a preference for bryophytes, and five occurred in the epibryon only. As regards moisture conditions, 15% of the taxa occurred on wet or temporarily dry sites, and 4% lived mostly outside water bodies. The main environmental factors influencing diatom assemblages were pH, conductivity, altitude, and shading. The carbonate-substratum crenic vegetation was composed of a mixture of vascular plants and bryophytes, which find their ecological optimum in springs. Bryophyte cover was dominant, with the most abundant taxa belonging to the genus Palustriella. The vegetation corresponded to the Cratoneuretum commutati association

Diatom species richness in Swiss springs increases with habitat complexity and elevation

Understanding the drivers of species richness gradients is a central challenge of ecological and biodiversity research in freshwater science. Species richness along elevational gradients reveals a great variety of patterns. Here, we investigate elevational changes in species richness and turnover between microhabitats in near-natural spring habitats across Switzerland. Species richness was determined for 175 subsamples from 71 near-natural springs, and Poisson regression was applied between species richness and environmental predictors. Compositional turnover was calculated between the different microhabitats within single springs using the Jaccard index based on observed species and the Chao index based on estimated species numbers. In total, 539 diatom species were identified. Species richness increased monotonically with elevation. Habitat diversity and elevation explaining some of the species richness per site. The Jaccard index for the measured compositional turnover showed a mean similarity of 70% between microhabitats within springs, whereas the Chao index which accounts for sampling artefacts estimated a turnover of only 37%. Thus, the commonly applied method of counting 500 valves led to an undersampling of the rare species and might need to be reconsidered when assessing diatom biodiversity

Is it possible to study paleoenvironmental changes in Alpine spring habitats? A few examples from the south-eastern Alps (NE Italy)

Palaeolimnological techniques were applied to spring habitats in the Trentino Region (NE Italy) as a test in order to reconstruct past environmental changes in these crucial and fragile milieus. Three different sites were selected from a database of more than one hundred on the basis of morphological, geological, and biological factors, including human impact evaluation: Nambrone, Paul and Madonnina Val Lomasona. Sampling was performed by adapting standard lake-sediment coring methods, and the retrieved sediment was described and subsampled following standard "lake" procedures. Field work and sedimentological analyses revealed clear influence from nearby fluvial environment for the Nambrone site, whereas Paul and Madonnina Val Lomasona were selected for further analyses (e.g., dating, diatoms, chironomids). Lead-210 and Caesium-137 dating methods were used to obtain a chronological framework, in addition to historical information on land use and other events in the area. The upper part of the Paul sequence presented organic rich sediment compatible with spring environments, but the lower and essentially detrital part appeared to record alluvial deposition, probably linked to extraordinary flood events (1882, 1966). This interpretation is indirectly confirmed by the records of the fallout nuclides Caesium-137 and Lead-210, that were both unfortunately concentrated in the topmost 1 cm, making it impossible to construct a normal age-depth profile. Madonnina Val Lomasona sedimentological and biological indicators point to a marked change around ca 5 cm, dividing the sequence in two units, corresponding to different environmental conditions. Although the interpretation of the dating results is not completely straightforward, the assembled data suggest that the upper 5 cm of the record represents ca the last 50 years. During this period we found typical limnocrenic, clear-water spring conditions, while before 1960s the coexistence of lotic and lentic chironomid species including several opportunistic ones and the low richness, emphasized the presence of a disturbance (e.g., highly variable flow and/or trophic conditions), as confirmed also by diatom assemblages and sedimentological features. The recorded disturbance is probably linked to a water-level change due to the local land use, as also testified by historical data. The results of this study support the idea that carefully selected spring sites might be approached with adapted palaeolimnological techniques to extract valuable palaeoenvironmental information. However, it also highlighted the low percentage of "good sites" (1%) and considerable difficulties in coring and sampling without disturbing the sediment